The examples within use this syntax because request matching is a function of the adapter and not the mocker.
All the same arguments can be provided to the mocker if that is how you use requests_mock within your project, and use the

mock.get(url,...)

form in place of the given:

adapter.register_uri('GET',url,...)

Note

By default all matching is case insensitive. This can be adjusted by
passing case_sensitive=True when creating a mocker or adapter or globally
by doing:

The most simple way to match a request is to register the URL and method that will be requested with a textual response.
When a request is made that goes through the mocker this response will be retrieved.

A dictionary of headers can be supplied such that the request will only match if the available headers also match.
Only the headers that are provided need match, any additional headers will be ignored.

As distinct from Custom Matching below we can add an additional matcher callback that lets us do more dynamic matching in addition to the standard options.
This is handled by a callback function that takes the request as a parameter:

Using this mechanism lets you do custom handling such as parsing yaml or XML structures and matching on features of that data or anything else that is not directly handled via the provided matchers rather than build in every possible option to requests_mock.

If you need more flexibility than provided by register_uri() then you can add your own matcher to the Adapter. Custom matchers can be used in conjunction with the inbuilt matchers. If a matcher returns None then the request will be passed to the next matcher as with using register_uri().